Something Rotten in Wisconsin!?!

By: Dave Scharfenberger, Certified Arborist WI-0131A

Summer 2004 Newsletter in Adobe PDF format Root rots and collar rots can cause both health and structural problems to trees.

Few things scare an arborist more than root rots and collar rots. They begin out of sight in the soil and can have a tree well into a death spiral by the time a homeowner notices.

Root Rots

This is a devastating group of soil borne fungus that attacks tree roots (usually of weakened trees). The dry conditions we had for the year and a half before this spring are the kind of situation that can set up root rot problems. Wet conditions like this spring then may be the final ingredient to allow this problem to aggressively kill tree roots.

Symptoms: The disease causes root death and the tree cannot absorb water and nutrients needed for normal plant growth, leading to indicators similar to those of general decline. The foliage turns yellow-green, is smaller and overall growth is stunted. Foliar scorch can take place during the summer while premature fall coloration and leaf drop can also occur.

A general dieback of twigs, to death of entire branches happens as the disease progresses. In some cases, mushrooms occur at the base of a tree or shoestring-like mats are present under the bark. Both are good signs of infection. Trees may decline slowly over several years or die suddenly. In extreme cases, the tree can be prone to wind throw due to the loss of anchoring.

Collar Rots

The main difference between collar rots and root rots is where the infection takes place. Collar rots occur in the root collar, which is the transition zone between the trunk and the root system. The pathogens are similar, the symptoms are the same and the results are just as deadly.

We as Arborists like to separate them because collar rots seem to be much more of an urban forestry problem due to the improper planting and maintenance techniques used by many people. Deep planting and excessive mounding of mulch around trunks of trees can allow a collar rot to occur where it never would without these improper practices. Girdling roots can also be associated with collar rots.


This can be a challenge, because the disease is in the roots and we cannot visually see the extent of the infection. There may be times that a tree is too far gone and yet all of the signs do not make that clear.

There are fungicides that can be used as a basal drench or as a granular treatment to the soil surface that can be very effective against these killer diseases. For root collar infections, opening up the root collar with the air spade can be critical to take away conditions that are favorable for the pathogen.

Just as important are watering when the soil dries out and fertilization, as the reduced root system will have a hard time picking up moisture and nutrients. Also important are soil treatments to encourage root growth because the tree will have to regrow lost roots to survive. Treatments such as mycorrhizae, bio-pak root stimulant, etc. can be very beneficial.

Experience and knowledge are critical when dealing with root or collar rot disease. That is what the Certified Arborists at Wachtel Tree Science and Service can supply.

© Copyright 2004 – Wachtel Tree Science & Service, Inc.

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